The rule here is simple.
Difference between attic and scuttle.
The bird will die after a few days if it can t get out.
The difference is pressure is most commonly created by a difference in temperature.
The goal with an unfinished attic is to seal it off from the main living space below.
For air to move there must a path hole in the ceiling crack in the drywall poorly sealed attic scuttle etc and a difference in pressure.
This means you should insulate between and over the floor joists.
As nouns the difference between hatch and scuttle is that hatch is a horizontal door in a floor or ceiling or hatch can be the act of hatching while scuttle is a container like an open bucket usually to hold and carry coal or scuttle can be a small hatch or opening in a boat also small opening in a boat or ship for draining water from open deck or scuttle can be a quick pace.
To make sure that it isn t just a gaping obvious hole in a ceiling it often has a removable.
Check this out for more info.
You can buy some poison to kill the squirrels or rats in a garden centre don t let them stay up there as they can do lots of damage to the wiring etc if they remain.
Don t forget to also insulate the attic hatch.